This invention relates to an image fiber used to transmit an image and a method of fabricating a base material for the image fiber.
An image fiber, which is also called "an image guide", is so constructed that the number of cores is densely arranged by suppressing the irregularity in the diameter as much as possible. The image fiber further prevents light from leaking by increasing the diameter of the core and the thickness of the cladding.
Two conventional representative examples of a method of fabricating an image fiber will be described. One of them includes the steps of arranging, as shown in FIG. 1, several thousands to several ten thousands of optical fiber strands 1, 1, 1, . . . (each strand having an inner core) of the same diameter so as to externally contact each other in case of filling the strands in a pipe of the same material as the strands, filling the strands thus arranged in the pipe, and then simultaneously drawing the strands 1, 1, 1, . . . together with the pipe under heated, thereby melting and integrating the strands. The other method includes the steps of filling optical fiber strands 1, 1, 1, . . . in a pipe, arranging the strands by a water stream or a supersonic vibration, and then simultaneously drawing the strands 1, 1, 1, . . . in the same manner as the first method.
FIG. 2 shows the strand filling state of the image fiber produced according to the foregoing methods. As is obvious in FIG. 2, when the strands 1, 1, 1, . . . are filled in the pipe 2 of quartz, air gap S is formed between the strands 1, 1, 1, . . . and the pipe 2.
When the image fiber of this state is collapsed or is directly drawn, the pipe 2 is reduced in its diameter, the pipe reducing force is applied only to the partial strands la, la in contact with the pipe 2 at the time of initially reducing the pipe 2. Accordingly, the arrangement of the strands 1, 1, 1, . . . is disorderly.
In this case, since the filling density of the strands 1, 1, 1, . . . is high and the arranging state is very stabilized, a great disorder of the arrangement does not occur, but as shown in FIG. 3, the arrangement is partially displaced, and cracked disorders (a dislocation of arrangement) 4, 4, 4, . . . occur among the arranging regions 3, 3, 3, . . . .
In the case of the image fiber thus obtained, the dislocations of the arrangement of the strands not only become an obstacle to the observation of the arrangement, but also cause a partial decrease in the quality of an image and, since the image fiber is formed in an arranging pattern, a moire occurs in the case that the image fiber is connected to a TV camera.
As is known, a moire occurs when the array of picture elements substantially coincides with the space frequency of a TV scanning line.